Washington — As President Obama’s administration makes a case for military action in response to Syria’s alleged use of chemical weapons against its own civilians, the discussion is prompting a key legal question: Does Mr. Obama have the authority to act without congressional approval or a UN Security Council resolution?

In England, Prime Minister David Cameron has recalled Parliament and asked for a government motion and vote on the appropriate British response.

But opinions are mixed about Obama’s need for similar backing. And the question is not only a legal one but also political. Legally, does Obama need congressional support? And politically, should he desire it?

Even though President George W. Bush’s administration ultimately had to defend the supporting evidence it produced – or misrepresented, depending on your view – to lobby for military action in Iraq, Congress did pass a war resolution in 2002 authorizing force.

In 1991, President George H.W. Bush also asked for and received congressional backing for the Gulf War waged on his watch. The UN Security Council passed a resolution as well, requiring Iraq to destroy its nuclear, chemical, and biological weapons arsenal and pay war reparations to Kuwait.

But the UN Security Council does not appear to be a viable avenue for the Obama administration as it considers how to move on Syria. The Russians, fellow members, have pledged to veto anything considered by the UN. Their comparisons between Obama and his predecessor, often deemed the cowboy diplomat by his opponents, are rampant.

“Obama is restlessly heading towards war in Syria like Bush was heading towards war in Iraq,” Alexei Pushkov, the head of the Russian lower house’s international committee, said on Twitter. “Like in Iraq, this war would be illegitimate and Obama will become Bush’s clone.”

Sergei Lavrov, the Russian foreign minister, added his voice to the mix: "The use of force without the approval of the United Nations Security Council is a very grave violation of international law.”

Of course, the Constitution provides Congress with the power to declare war. But the Obama administration would likely argue it’s not proposing war, just, potentially, a missile strike that would represent a slap to the regime of President Bashar al-Assad and caution that there’s more where that came from. An effort to dislodge him, but not a full commitment of troops, money, and time.

But some lawyers see danger signs in Obama’s push for strikes against Syria. Obama is advocating an “imperial presidential model,” says Jonathan Turley, a professor of public interest law at George Washington University.

“We speak of United Nations support but we continue to act unilaterally in making war on those countries who do not yield to our demands,” Professor Turley says. “The talk of unilateral military action reaffirms the view that the United States only acts within international rules when it suits our objectives.”

Congress is out of session this month, and given the seemingly irreparable fissure between the GOP-controlled House of Representatives and the White House, it’s unclear, if probably also unlikely, that the executive branch and lawmakers could reach consensus on how to proceed in Syria. At least not in a timely fashion.

Congressional approval would give Obama political cover, but it doesn’t appear to be in the cards.

“Legally the president is on very firm ground if he seeks congressional authorization,” says Wells Bennett, a national security law fellow at Brookings. “The question then becomes is that doable as a political matter.”

With the situation in Syria fluid, what then might Obama use as backing?

Mr. Bennett says the president’s powers to act independently loosely encompass several areas: national security, national interest in providing for regional stability, and protection of US property or persons. A claim of self-defense, another possible support for executive action, isn’t evident in this situation.

More likely, where Syria is concerned, the administration is clearly considering the humanitarian principles involved and the tenuous balance that seems to be slipping away in this fraught region. With this rationale, the administration might reasonably make the claim that action is “morally and strategically justified,” Bennett says.

He also says the most likely, though by no means perfect, historic parallel is the 1999 NATO air campaign in Kosovo. Then, as now, civilians were involved in atrocities perpetrated by the government in power. Russia had ties, too, to Slobodan Milosevic’s regime, so President Clinton was unable to secure a UN resolution. Instead, he used NATO backing as endorsement for US air strikes.

Kosovo was a serious humanitarian crisis requiring expedited action; the Obama administration is making a similar claim for Syria.

“The trouble is that the legality of the Kosovo action was and remains acutely controversial, too – domestically, because the president acted alone, without a self-evident basis for doing so and without announcing his legal rationale publicly,” Bennett says, “and internationally, because (again) the Security Council did not sign off and no self-defense claim was implicated there, either. So Clinton’s actions were certainly controversial legally, then as now.”

Much as Obama’s are bound to be when, and if, he moves forward. The president likes to echo his predecessor, President Harry Truman, in stipulating that the buck stops with him. In the case of the Syria firestorm and US reaction to it, that couldn’t be more true.